1. Field of the Invention
The present invention relates to a method for visualizing a doped structure in an undoped environment using a microscope lens.
2. State of the Art
An example of a doped structure in an undoped environment is a core of doped silica glass in a monomode fiber comprised of a jacket of undoped silica glass that surrounds such a core.
Optical transmission links with monomode fibers make particular demands of the quality and reproducibility of fiber splices. In order to assure a constantly high quality of such splice connection, a careful alignment of the fiber cores before and during the actual splicing operation is necessary. One prior art method for aligning the fiber cores is the minimization of the transition attenuation given longitudinal transirradiation of the splice location. This method requires high outlay for coupling the monitoring beam in and out. Methods are therefore required wherein the cores of monomode fibers can be made visible with transillumination perpendicular to the fiber axis so that a visual alignment is enabled.
Microscopy at monomode fiber cores, however, is problematical because the core of monomode fibers as well as the surrounding material are highly transparent to visible light. The phase fronts of a light wave perpendicularly traversing the core are only slightly deformed by the small refractive index difference, which amounts to about 0.1%, and by the small core diameter. Such slight phase differences can be converted into usable light/dark contrast in the microscope image only with great outlay.
Such analysis applies generally to transparent doped structures in a transparent undoped environment.